If you are doing in-depth research on a particular piece of legislation start with a compiled legislative history. If you just need to find the full-text of a particular piece of legislative history and have a citation, start with the Sources of Legislative History Chart.
A compiled legislative history is a detailed inventory of legislative source documents for a particular law put together by a commercial publisher, interested researcher or other third party. It is extremely useful for the researcher as it has the full-text, or citations to, the most important legislative documents, such as committee reports. It will save you an enormous amount of time if you find a compiled legislative history for the public law you are interested in researching.